VERITAS File System 3.5 (HP OnlineJFS/JFS 3.5) Administrator's Guide (August 2003)

Chapter 2
VxFS Performance: Creating, Mounting, and Tuning File Systems
Kernel Tunables
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Kernel Tunables
This section describes the kernel tunable parameters in VxFS. All kernel tunables can be set or changedusing
the sam or kctune commands (see the sam(1M) and kctune(1M) manual pages).
Internal Inode Table Size
VxFS caches inodes in an inode table. The kernel tunable vx_ninode determines the number of entries in the
inode table.
vx_ninode is a static tunable that is initialized when VxFS is loaded, so any changes to vx_ninode cannot take
effect until the next system reboot.
By default, the initial value of vx_ninode is zero; the file system later computes a value based on the system
memory size.
The following example shows how to change the value of vx_ninode to 1,000,000:
# kctune –s vx_ninode=1000000
VxFS Buffer Cache High Water Mark
VxFS maintains its own buffer cache in the kernel for frequently accessed file system metadata. This cache is
different from the HP-UX kernel buffer cache that caches file data. The size of the VxFS buffer cache,, that is,
the maximum amount of memory that can be used to cache VxFS metadata, is determined by the
vxfs_bc_bufhwm tunable parameter.
By default, the initial value of vxfs_bc_bufhwm is zero ; the file system later computes a value based on the
system memory size. The value of vxfs_bc_bufhwm is specified in kilobytes. The minimum acceptable value is
6144 kilobytes. The following example sets the VxFS buffer cache high water mark to 300,000 kilobytes.
# kctune –s vxfs_bc_bufhwm=300000.
Typically, the default value computed by VxFS based on the amount of system memory ensures good system
performance across a wide range of applications. For application loads that cause frequent file system
metadata changes on the system (for example, a high rate of file creation or deletion, or accessing large
directories), changing the value of vxfs_bc_bufhwm may improve performance.
You can use the vxfsstat command to monitor buffer cache statistics and inode cache usage (see the vxfsstat
(1M) manual page).
Number of Links to a File
In VxFS, the number of possible links to a file can be configured by the vx_maxlink tunable.
vx_maxlink is a static tunable that is initialized when VxFS is loaded, so any changes to vx_maxlink cannot
take effect until the next system reboot. The default value of vx_maxlink is 32767, the maximum value is 65534.
The following example sets the maximum number of links to a file to 40,000:
# kctune –s vx_maxlink=40000